High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular, adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy $h\left(T\right)$ and on the specific heat capacity $c_p\left(T\right)$, has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3′,4′,5′-tetrafluoro[1,1′-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a low-temperature ferroelectric nematic phase ($N_F$) and a high-temperature paraelectric nematic phase $\left(N\right)$. However, in DIO these two phases are separated by an intermediate phase ($N_x$). From the detailed data of $h\left(T\right)$ and $c_p\left(T\right)$, we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO ($x_{\mathrm{DIO}}$). The $x_{\mathrm{DIO}}$ dependence on the transition temperatures for both transitions could be well described by a quadratic function. Both these transitions were weakly first order. The true latent heat of the $N_x\text{−}N$ transition of DIO was as low as $L=0.0075\pm 0.0005\mathrm{J}/\mathrm{g}$ and $L=0.23\pm 0.03\mathrm{J}/\mathrm{g}$ for the $N_F\text{−}{N}_x$ transition, which is about twice the previously reported value of 0.115 J/g for the $N_F\text{−}N$ transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing $x_{\mathrm{DIO}}$. At all the $N_x\text{−}N$ transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the $N_F$ to the higher-temperature phase exhibits substantial pretransitional behavior, in particular, in the high-temperature phase. Power-law analysis of $c_p\left(T\right)$ resulted in an effective critical exponent $\alpha =0.88\pm 0.1$ for DIO and this value decreased in the mixtures with decreasing $x_{\mathrm{DIO}}$ toward $\alpha =0.50\pm 0.05$ reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis.

An achiral compound, DIO, known to exhibit three nematic phases namely N, N_X and N_F, is studied by polarizing microscopy and electro-optics for different surface conditions in confinement. The high temperature N phase assigned initially as a conventional nematic phase, shows two additional unusual features: the optical activity and the linear electro-optic response related to the polar nature of this phase. An appearance of chiral domains is explained by the spontaneous symmetry breaking arising from the saddle-splay elasticity and followed by the formation of helical domains of the opposite chirality. This is the first example of helical segregation observed in calamitic non-chiral molecules in the nematic phase. As reported previously, the ferronematic N_F shows strong polar azimuthal surface interaction energy which stabilizes a homogeneous structure in planar aligned LC cells rubbed parallel and exhibits a twisted structure in cells with antiparallel buffing. The transmission spectra are simulated using Berreman's 4 × 4 matrix method. The observed agreement between the experimental and the simulated spectra quantitatively confirms the presence of twisted structures in antiparallel rubbed cells.

Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae) is an important economic pest and has a worldwide distribution. In Chile, this species has been reported over a large geographical area and is associated with tomato production. Although several plants have been described as hosts of the whitefly, this insect’s behavior against multiple hosts is still unclear. Therefore, the objective of our work was to identify the host plants, behaviors, preferences, performance, and choices of T. vaporariorum. First, over one year, we monitored nine production sites where tomato is the principal crop and identified 50 host plants belonging to 27 families, mostly Asteraceae and Solanaceae. Among the plants, those that were most infested by greenhouse whiteflies comprised Solanum lycopersicum, Phaseolus vulgaris, Cucurbita maxima, Malva sylvestris, Bidens aurea, and Sonchus oleraceus. In laboratory tests, greenhouse whiteflies showed a greater preference for S. oleraceus, S. lycopersicum, and P. vulgaris. The highest population growth rate was observed for B. aurea, followed by S. lycopersicum and S. oleraceus. Significant differences were found in the pairwise choice test, showing a greater preference for C. maxima and S. lycopersicum. Although this pest tends to choose tomatoes, this crop was not always the first choice in terms of preference and performance. This information is necessary for the development of integrated whitefly management programs that include adjacent habitats.

Nematic–nematic transitions in a highly polar nematic compound are studied, in thick cells in which the molecules are aligned parallel to the substrates but perpendicular to the applied electric field, using dielectric spectroscopy in the frequency range 1 Hz to 10 MHz over a wide temperature range. The studied compound displays three nematic phases under cooling from the isotropic phase: ubiquitous nematic N; high polarizability N_X; and ferroelectric nematic N_F. Two collective processes were observed. The dielectric strength and relaxation frequency of one of the processes P₂ showed a dependence on the thickness of the cell. The process P₁ is the amplitude mode, while the process P₂ is the phason mode.

A new mesogenic non-symmetric dimeric monomer with a terminal olefin function, forming a twist bend nematic (N_tb) as well as a nematic (N) phase, was synthesized, using an enhanced synthetic methodology, which avoids isomerization of the terminal double bond in the preparation of the dimer. This monomer was attached to a pentamethyldisiloxane group, resulting in the SmA LC phase behavior of the ensuing material. Linking the monomer to a siloxane main chain resulted in nematic phase behavior. Detailed studies with the N_tb phase forming dimer DTC5C7 show full miscibility of the dimer and the new LC polymer in the LC state, suggesting that the side-chain LC polymer forms a N_tb phase as the low-temperature nematic phase. Copolymerizing the monomer with a cyanobiphenyl-based monomer allows us to tune the glass transition and phase behavior further.